Diffusion in Liquids


Concepts Shown:

atomic vibrations and diffusion


two large clear glass beakers, red food coloring, hot water, cold water, pipet


  1. Fill the first beaker with hot water, the second with cold.
  2. Discuss atomic/molecular vibrations and the effect of temperature on these molecular (H2O) vibrations. Ask students to reason which beaker will allow the red food coloring to diffuse faster.
  3. Add the food coloring to each beaker using the pipette. Note the food coloring in the hot water diffuses faster.

The average kinetic energy of the atoms and/or molecules increases, roughly, in proportion to the absolute temperature: [eq] As the temperature increases, the diffusivity increases. Therefore, the water molecules of the hot water have more kinetic energy than the cold ones, and they oscillate more rapidly. This is evidenced by how much quicker the food coloring diffuses in the hot water. The molecular vibrations create momentary holes for the food coloring atoms to diffuse through. Remarks: If you have time, try adding a more viscous liquid than food coloring. This would show the effects of different Do's.


Roberta Dean

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